1. Field of the Invention
The present invention relates to an organic electroluminescence (EL) device, and more particularly, to an organic EL device, which has a heat dissipation structure to dissipate heat generated upon driving of the organic EL device and heat from a thin film transistor (TFT) on a substrate thereof.
2. Discussion of the Related Art
Generally, an organic EL device is a device which employs electroluminescence of an organic material, and has been spotlighted as a light emitting device capable of emitting light of high brightness while being driven by low voltage direct current, in which an organic light emitting layer or an organic hole transfer layer is stacked between an upper electrode and a lower electrode.
FIGS. 1A and 1B are a cross-sectional view and a plan view illustrating a conventional organic EL device, in particular, a conventional Active matrix bottom emission type organic EL device, respectively.
As shown in FIGS. 1A and 1B, the organic EL device comprises: a transparent substrate 10 which is composed of ITO and has a TFT 10′ and a first electrode 10″ formed thereon; at least one organic material layer 11 which comprises a hole injection layer, a hole transfer layer, a light emitting layer, a electron transfer layer, etc.; a second electrode 12 for injection of electrons and reflection of emitted light; a sealant 13 for sealing the components; and a seal-cup 14.
When + and − direct voltage is applied to the first electrode 10″ and the second electrode 12 of the Active matrix bottom emission type organic EL device constructed as described above, holes injected from the first transparent electrode 10″ transfer to the light emitting layer through the hole transfer layer of the organic material layer 11. In addition, electrons injected from the second electrode 12 transfer to the light emitting layer through the electron transfer layer. As a result, combination of the holes and the electrons occurs in the light emitting layer so that light is emitted through the transparent substrate made of ITO. In order to prevent cell shrinkage in the organic EL device due to moisture in atmosphere, the organic EL device is sealed by the sealant 13 and the seal-cup 14 in N2 atmosphere, so that the moisture in the atmosphere is prevented from penetrating into the device. In most cases, the second electrode 12 is deposited inside a sealing line 13′ which is on an active region, and used as a common electrode.
In such an active matrix bottom emission type organic EL device, heat generating regions can be generally divided into the TFT 10′ which is formed on the substrate, and the organic material layer 11 of the organic EL device. At this time, the generated heat can be dissipated from the device to the outside thereof via heat conduction through a line for supplying electric power, and the glass substrate through which light is emitted, and via convection of gas existing between the second electrode 12 and the seal-cup 14 of the organic EL device.
However, the conventional organic EL device as described above has disadvantages in that an increase in width of the line results in reduction of an aperture ratio, in that the glass substrate causes ineffective heat transfer, and in that nitrogen occupying most portions of the gas is not conducive to dissipation of heat due to its significantly low heat conductivity. As such, the heat is not dissipated to the outside, and increases an interior temperature of the device, causing degradation in performance of the TFT, deposition of the organic material, and degradation in interface properties between the organic material and the electrode. As a result, the conventional organic EL device has problems of instability and reduced lifetime. In this point of view, there is a need in the art to provide an effective dissipation system in the organic EL device.